Structural study by X-ray diffraction and Mössbauer spectroscopy of a new synthetic iron phosphate: K4MgFe3(PO4)5

A new iron phosphate K4MgFe3(PO4)5 has been synthesized by the flux method and characterized by single-crystal X-ray diffraction and Mössbauer spectroscopy. It crystallizes in the tetragonal system with the space group P4¯21c and the unit cell parameters a=9.714(3) Å and c=9.494(5) Å. The crystal structure is of a new type. It exhibits a three-dimensional framework built up from corner-sharing MO5 (M=0.75Fe+0.25Mg) trigonal bipyramids and PO4 tetrahedra. The K+ ions are occupying large eight-sided tunnels running along c. A room temperature Mössbauer study confirmed the +3 valence state of iron and its five-coordination.